1. Technical Field
The present invention relates to wireless communication, and more particularly to a suppressor having a bandpass filtering function.
2. Related Art
In recent years, breakthrough in wireless communication technology has contributed both considerable convenience and infinite business opportunities. Among others, the most popular and widely-used wireless communication technology is the 802.11b/g standard established by the Institute of Electrical and Electronics Engineers (IEEE). A working frequency of the IEEE 802.11b/g standard is 2.4 GHz. In a wireless communication circuit the filter is an essential and indispensable component. A main function of the filter is to maintain purity of a main frequency signal and remove signals that are not at the main frequency. For example, for the IEEE 802.11b/g standard, the main frequency is 2.4 GHz.
An ideal filter has the following features: a passband has no attenuation, but attenuation is infinitely great within a cutoff frequency, and that a jump of the passband and the cutoff frequency should be as steep as possible. In addition, a signal at the main frequency further carries a second harmonic at a frequency of 4.8 GHz and a third harmonic at a frequency of 7.2 GHz. The second harmonic and the third harmonic render the wireless communication circuit unable to satisfy the limitations and requirements of standards and regulations for the frequency bands.
The wireless communication product development trend is towards light, thin, short, and small products. A huge challenge in the filter design in the prior art is decreasing an area occupied by the filter while ensuring filter efficiency. Another aspect, electromagnetic interference (EMI), must also be considered seriously, as a wireless communication product is usually used outdoors. In order to avoid damage to elements in a wireless communication circuit due to an induction current caused by lightning, an EMI suppressor is often added in the wireless communication product to protect the elements in the wireless communication circuit. The EMI suppressor usually needs a large area to achieve a desirable anti-EMI effect. Therefore, maintaining a desirable effect of the EMI suppressor and decreasing an area of the EMI suppressor at the same time is a problem urgently awaiting a solution.